One of the more serious concerns of telephone companies is the prevention of moisture penetration into outside cable plant. For the past fifteen to twenty years the main defensive mechanism has been the use of "pressurization". Pressurization has proven invaluable; however, as it is a physical system, it is limited by the pneumatic resistance of the cable and is often difficult to maintain. Due to practical considerations the use of air pressure protection systems is limited to the larger feeder and trunk cables. In instances where filled telecommunication cables are used in conjunction with non-filled cable types, pressurization can be extremely difficult if not physically impossible. The monitoring and protection system described within is an electronic system and therefore not subject to the constraints limiting a physical protection system such as pressurization. The invention offers much in simplicity and economy and may be incorporated in all types of cable plants, cables large and small, filled and unfilled.
The invention as designed, does not prevent or retard the ingress of moisture. It does, however, react instantly to its presence and provides for pin-pointing the location of the breach. Except in cases of catastrophic failure, the system provides warning and facilitates remedial action before outages occur.
The present invention is an electronic system which continuously monitors outside cable plant for the presence of moisture in cables or at splices, repeater sites, and other critical locations. At the first trace of moisture an alarm is activated and the system indicates clearly whether the cause is a cable sheath or other fault. The general monitoring system operates over a special moisture detection tape which is an integral part of the cable construction.
In accordance with the invention there is provided apparatus for monitoring electrical cables and specific locations therealong, such as splice joints and the like, against the ingress of moisture and including a source of electrical power; comprising in combination a pair of main separate and dielectrically isolated monitoring conductors operatively installed along the cable being monitored and being operatively connected to the source of electrical power, a terminating resistor across the distal ends of said monitoring conductors to ensure continuity of current through said monitoring conductors, thereby verifying the continuity thereof, and electronic detection means operatively connected to said monitoring conductors, said electronic detection means including indicating means to signal a lack of current continuity through said monitoring conductors and further indicating means to signal an increase of current flowing in said monitoring conductors, beyond a predetermined value due to a lessening of the resistance of the insulating dielectric between the two monitoring conductors, as by the presence of moisture.
A further advantage of the invention is to provide a device of the method and character herewithin described which is well suited to the purpose for which it is designed.